Electrochemical device and electronic device

Abstract

The invention provides an electrochemical device and an electronic device. The electrochemical device comprises: a negative electrode comprising a negative electrode current collector, the surface of which is provided with a negative electrode active material layer; the positive electrode comprises a positive electrode current collector, a positive electrode active material layer is arranged on the surface of the positive electrode current collector, and an insulating layer is arranged on the surface of one side, close to the tab part, of the positive electrode current collector; an isolating membrane; wherein the outer end edge of the negative electrode active material layer is closer to the outer side than the outer end edge of the positive electrode active material layer facing the negative electrode active material layer; the inner end edge of the insulating layer is connected with or partially coincides with the outer end edge of the positive electrode active material layer, and the outer end edge of the insulating layer is flush with the outer end edge of the negative electrode active material layer or is closer to the outer side than the outer end edge of the negative electrode active material layer. According to the invention, burrs and material falling generated by punching can be reduced, the impedance of the edge area of the negative electrode is effectively reduced, the edge dynamics of the negative electrode is improved, the edge lithium precipitation of the negative electrode is improved, and the ignition or explosion probability of the electrochemical device is reduced.

Description

[0001] This application is a divisional application with application number 202180003251.3, application date February 18, 2021, and invention name “Electrochemical device and electronic device”. Technical Field

[0002] The present application relates to an electrochemical device and an electronic device. Background Art

[0003] Electrochemical devices, such as lithium-ion batteries, are widely used in electronic products such as communications equipment, laptops, digital cameras, and electric vehicles due to their high specific energy, lack of memory effect, and environmental friendliness. However, with the rapid development of technology and the diversification of market demands, higher performance requirements, such as safety, are being placed on electrochemical devices.

[0004] There are many factors that affect the safety performance of lithium-ion batteries. For example, when the preparation process of wound lithium-ion batteries involves the electrode punching process, the risk of burrs and material falling off on the edges of the die used for punching increases with the frequency of use. If burrs or material fall off on the electrode during the punching process, it may pierce the diaphragm and cause a short circuit, thereby posing a safety risk. For another example, lithium plating in the battery may increase the chance of battery fire or explosion, thereby posing a safety risk. Summary of the Invention

[0005] In some embodiments, the present application provides an electrochemical device comprising: a negative electrode, comprising a negative electrode current collector, wherein a negative electrode active material layer is provided on the surface of at least one side of the negative electrode current collector; a positive electrode, comprising a positive electrode current collector, wherein a positive electrode active material layer is provided on the surface of at least one side of the positive electrode current collector, and an insulating layer is provided on the surface of the positive electrode current collector on the side close to the pole ear portion, wherein the pole ear portion is formed by cutting the empty foil area at the edge of the positive electrode current collector, and the pole ear portion protrudes from the positive electrode current collector; a separator, which is arranged between the negative electrode and the positive electrode, and the positive electrode active material layer and the negative electrode active material layer face each other with the separator separated; wherein the outer edge of the negative electrode active material layer is further outward than the outer edge of the positive electrode active material layer at the facing position; the inner edge of the insulating layer is in contact with or partially overlaps with the outer edge of the positive electrode active material layer, the outer edge of the insulating layer is flush with the outer edge of the negative electrode active material layer or further outward than the outer edge of the negative electrode active material layer, and the thickness T of the insulating layer i The thickness T of the positive electrode active material layer p Satisfy: 0μm≤T p –T i ≤10μm.

[0006] In some embodiments, the insulating layer is provided on a surface of the positive electrode current collector away from the electrode ear portion.

[0007] In some embodiments, a width A of a portion where the outer edge of the insulating layer extends beyond the outer edge of the negative electrode active material layer satisfies: A≤3 mm.

[0008] In some embodiments, the width A' of the insulating layer satisfies: 0.2 mm ≤ A' ≤ 10 mm.

[0009] In some embodiments, a width B of a portion where the outer edge of the negative electrode active material layer exceeds the outer edge of the positive electrode active material layer satisfies: 0.2 mm ≤ B ≤ 5 mm.

[0010] In some embodiments, the thickness of the insulating layer T i The thickness T of the positive electrode active material layer p Satisfy: 0μm≤T p –T i ≤2μm.

[0011] In some embodiments, the thickness of the insulating layer T i Satisfy: 10μm≤T i ≤T p .

[0012] In some embodiments, the insulating layer includes an inorganic material and an adhesive, wherein the inorganic material includes at least one of barium sulfate, calcium silicate, aluminum oxide, boehmite, magnesium hydroxide, aluminum hydroxide, silicon dioxide, magnesium oxide, and calcium orthosilicate, and the adhesive includes at least one of polyvinylidene fluoride, polyurethane, polyacrylate, styrene-butadiene rubber, polyetherimide, sodium carboxymethyl cellulose, or acrylate.

[0013] In some embodiments, based on the total weight of the insulating layer, the weight percentage of the inorganic material is 60% to 93%, and the weight percentage of the binder is 7% to 40%.

[0014] In some embodiments, the impedance of the insulating layer is greater than or equal to 1 KΩ.

[0015] The present application also provides an electronic device, which includes the aforementioned electrochemical device of the present application. The technical solution of the present application has at least the following beneficial effects: the insulating layer provided in the electrochemical device of the present application can reduce burrs and material dropouts caused by punching, and can also provide support for the edge region of the negative electrode active material layer, so that the edge region of the negative electrode active material layer and the separator can be more tightly bonded, reducing the impedance of the negative electrode edge region, improving the negative electrode edge dynamics, improving the negative electrode edge lithium deposition, reducing the probability of fire or explosion of the electrochemical device, and improving the safety performance of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1( a ) is a cross-sectional view of a portion of an electrode body according to an embodiment of the present application, FIG1( b ) is an exploded view of FIG1( a ), and FIG1( c ) is a schematic diagram of a portion of the electrode body according to the present embodiment as viewed from the positive electrode side;

[0017] FIG2( a ) is a cross-sectional view of a portion of an electrode body according to another embodiment of the present application, FIG2( b ) is an exploded view of FIG2( a ), and FIG2( c ) is a schematic diagram of a portion of the electrode body according to this embodiment as viewed from the positive electrode side;

[0018] FIG3( a ) is a cross-sectional view of a portion of an electrode body according to another embodiment of the present application, FIG3( b ) is an exploded view of FIG3( a ), and FIG3( c ) is a schematic diagram of a portion of the electrode body according to this embodiment as viewed from the positive electrode side;

[0019] FIG4( a ) is a partial cross-sectional view of an electrode body in another embodiment of the present application, FIG4( b ) is an exploded view of FIG4( a ), and FIG4( c ) is a schematic diagram of a portion of the electrode body of this embodiment viewed from the positive electrode side;

[0020] FIG5( a ) is a cross-sectional view of a portion of an electrode body in another embodiment of the present application, FIG5( b ) is an exploded view of FIG5( a ), and FIG5( c ) is a schematic diagram of a portion of the electrode body of this embodiment viewed from the positive electrode side;

[0021] The figures are marked as: positive electrode 10, positive electrode current collector 11, positive electrode active material layer 12, outer edge 12a of the positive electrode active material layer, insulating layer 13, outer edge 13a of the insulating layer, inner edge 13b of the insulating layer, overlapping portion 14 of the positive electrode active material layer and the insulating layer, negative electrode 20, negative electrode current collector 21, negative electrode active material layer 22, outer edge 22a of the negative electrode active material layer, separator 30, and pole ear portion 40. DETAILED DESCRIPTION

[0022] It will be understood that the disclosed embodiments are merely examples of the present application, which can be implemented in various forms. Therefore, the specific details disclosed herein should not be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to implement the present application in various ways.

[0023] In the description of this application, it should be understood that the terms "length", "width", "thickness", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on this application.

[0024] (Electrochemical Device)

[0025] The electrochemical device of the present application is, for example, a primary battery, a secondary battery, a fuel cell, a solar cell, or a capacitor. The secondary battery is, for example, a lithium secondary battery, including but not limited to a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0026] In some embodiments, an electrochemical device includes a negative electrode, a positive electrode, and a separator.

[0027] Please refer to Figure 1(a) to Figure 5(c) The negative electrode 20 includes a negative electrode current collector 21, and a negative electrode active material layer 22 is provided on the surface of at least one side of the negative electrode current collector 21; the positive electrode 10 includes a positive electrode current collector 11, and a positive electrode active material layer 12 is provided on the surface of at least one side of the positive electrode current collector 11; the isolation membrane 30 is arranged between the negative electrode 20 and the positive electrode 10, and the positive electrode active material layer 12 and the negative electrode active material layer 22 face each other across the isolation membrane 30; the outer end edge 22a of the negative electrode active material layer is further outward than the outer end edge 12a of the positive electrode active material layer in the facing position.

[0028] In order to clearly describe the various directions, Figure 1(a) to Figure 5(c) The width direction (indicated by W in the figure) and the thickness direction (indicated by T in the figure) are shown in the figure. The width direction is relative to the length direction. Taking the strip-shaped positive electrode of the wound battery as an example, the extension direction of the long side of the long rectangular positive electrode collector is regarded as the length direction, and the width direction is perpendicular to the length direction. Figure 1(a) to Figure 5(c) As shown, at both ends in the width direction, the end edge of the positive electrode active material layer 12 close to the edge of the positive electrode current collector is the outer edge 12a of the positive electrode active material layer, and the end edge of the negative electrode active material layer 22 close to the edge of the negative electrode current collector is the outer edge 22a of the negative electrode active material layer.

[0029] In order to prevent the battery from short-circuiting and ensure that the lithium ions released from the positive electrode active material layer 12 can be completely received by the negative electrode active material layer 22, so as to avoid the safety risk of lithium plating caused by the part of the positive electrode active material layer 12 that exceeds the negative electrode active material layer 22, the width of the negative electrode active material layer 22 is designed to be greater than the width of the positive electrode active material layer 12, so that there is an overhang area on the negative electrode sheet. In this application, the outer edge 22a of the negative electrode active material layer is designed to be further outward than the outer edge 12a of the positive electrode active material layer in the facing position. In some embodiments, the width B of the part where the outer edge 22a of the negative electrode active material layer exceeds the outer edge 12a of the positive electrode active material layer satisfies: 0.2mm≤B≤5mm. In some embodiments, the width B of the part where the outer edge 22a of the negative electrode active material layer exceeds the outer edge 12a of the positive electrode active material layer satisfies: 0.5mm≤B≤5mm. In some embodiments, the width B of the portion where the outer edge 22 a of the negative electrode active material layer exceeds the outer edge 12 a of the positive electrode active material layer is: 0.8 mm ≤ B ≤ 2 mm.

[0030] However, the inventors found that when the width of the negative electrode active material layer 22 is greater than that of the positive electrode active material layer 12, the impedance near the negative electrode active material layer 22 corresponding to the outer edge 12a of the positive electrode active material layer is large, which reduces the kinetics of the negative electrode edge area, makes lithium deposition more likely, and creates a safety risk. If the method of reducing the charge rate is used to reduce the impedance generated by polarization during the negative electrode charging process, although lithium deposition at the negative electrode edge can be avoided, reducing the charge rate will prolong the charging time, greatly reducing the customer experience and product competitiveness; if the kinetics of the negative electrode active material is improved, the proportion of the negative electrode active material is increased, CMC-Li (carboxymethyl cellulose lithium) is used instead of CMC-Na (carboxymethyl cellulose sodium), or a binder with better kinetics is used, such as using a styrene-acrylic binder instead of a styrene-butadiene rubber binder to improve the kinetics of the negative electrode edge area, although there is a certain effect, improving the kinetics by these methods has reached a bottleneck period and it is difficult to continue to improve on the existing basis.

[0031] The present application sets an insulating layer 13 on the positive electrode current collector 11, and by setting the position and size relationship of the insulating layer 13, the positive electrode active material layer 12 and the negative electrode active material layer 22, it is possible to reduce the impedance of the negative electrode edge area, improve the negative electrode edge dynamics, improve the lithium deposition at the negative electrode edge, and reduce the probability of fire or explosion of the electrochemical device.

[0032] The insulating layer 13 may be provided only on the surface of the positive electrode current collector 11 close to the electrode ear 40 , or may be provided on both the surface of the positive electrode current collector 11 close to the electrode ear 40 and the surface of the positive electrode current collector 11 away from the electrode ear 40 .

[0033] In this application, the tab 40 refers to the empty foil area at the edge of the current collector reserved during electrode coating. In some embodiments, the tab 40 protrudes from the current collector. After rolling and slitting, the empty foil area at the edge of the current collector is trimmed before winding to form the tab.

[0034] In some embodiments, as Figure 1(a) to Figure 1(c) In the illustrated portion of the electrode body, an insulating layer 13 is provided on the surface of the positive electrode current collector 11 near the electrode ear portion 40. The inner edge 13b of the insulating layer is in contact with the outer edge 12a of the positive electrode active material layer. The outer edge 13a of the insulating layer is further outward than the outer edge 22a of the negative electrode active material layer. In some embodiments, as Figure 2(a) to Figure 2(c) In the illustrated portion of the electrode body, an insulating layer 13 is provided on the surface of the positive electrode current collector 11 close to the electrode ear 40, the inner edge 13b of the insulating layer is in contact with the outer edge 12a of the positive electrode active material layer, and the outer edge 13a of the insulating layer is flush with the outer edge 22a of the negative electrode active material layer.

[0035] At this time, since an insulating layer 13 is provided on the surface of the positive electrode current collector 11 on one side close to the pole ear portion 40, when the pole piece provided with the insulating layer 13 is punched, the burrs and material falling caused by punching can be effectively reduced, thereby improving the safety performance of the electrochemical device; at the same time, at one end side close to the pole ear portion 13, since an insulating layer 13 is provided on the positive electrode 10, and the inner edge 13b of the insulating layer is connected to the outer edge 12a of the positive electrode active material layer, the outer edge 13a of the insulating layer is closer to the outside than the outer edge 22a of the negative electrode active material layer or the outer edge 13a of the insulating layer is flush with the outer edge 22a of the negative electrode active material layer. Therefore, during the electro-pressure formation, the insulating layer 13 of the positive electrode on this end side can provide support for the edge area of the negative electrode active material layer, so that the edge area of the negative electrode active material layer and the isolation membrane can be more tightly combined, thereby reducing the impedance of the negative electrode edge area and improving the dynamics of the negative electrode edge area. If the outer edge 13a of the insulating layer is closer to the inside than the outer edge 22a of the negative active material layer, the edge of the negative active material layer 22 that extends beyond the insulating layer is in a suspended state. When the battery is pressurized, the bond between the extending portion and the isolation membrane is not tight enough, the electron transmission distance is large, the impedance is large, and lithium deposition is easy.

[0036] During the slurry coating process, when the slurry of the insulating layer 13 and the slurry of the positive electrode active material layer 12 are coated on the surface of the positive electrode current collector 11, the insulating layer slurry is coated along the edge of the positive electrode active material layer slurry. The slurry of the insulating layer and the slurry of the positive electrode active material layer may partially overlap, forming an overlapping portion 14 of the positive electrode active material layer 12 and the insulating layer 13. In some embodiments, Figure 3(a) to Figure 3(c)In the illustrated portion of the electrode body, an insulating layer 13 is provided on the surface of the positive electrode current collector 11 near the electrode ear portion 40. The inner edge 13b of the insulating layer partially overlaps with the outer edge 12a of the positive electrode active material layer, and the outer edge 13a of the insulating layer is further outward than the outer edge 22a of the negative electrode active material layer. In some embodiments, as Figure 4(a) to Figure 4(c) In the illustrated portion of the electrode body, an insulating layer 13 is provided on the surface of the positive electrode current collector 11 close to the electrode ear portion 40, the inner edge 13b of the insulating layer partially overlaps with the outer edge 12a of the positive electrode active material layer, and the outer edge 13a of the insulating layer is flush with the outer edge 22a of the negative electrode active material layer.

[0037] In some embodiments, as Figure 5(a) to Figure 5(c) In the illustrated portion of the electrode body, an insulating layer 13 is provided on the surface of the positive electrode current collector 11 on one side close to the electrode ear 40 and on the surface of the side away from the electrode ear 40. The inner edge 13b of the insulating layer is connected to the outer edge 12a of the positive electrode active material layer, and the outer edge 13a of the insulating layer is further outward than the outer edge 22a of the negative electrode active material layer.

[0038] When the insulating layer 13 is provided on both the surface of the positive electrode current collector 11 on the side close to the pole ear portion 40 and the surface of the positive electrode current collector 11 on the side away from the pole ear portion 40, the inner edge 13b of the insulating layer may also partially overlap with the outer edge 12a of the positive electrode active material layer, and the outer edge 13a of the insulating layer may also be flush with the outer edge 22a of the negative electrode active material layer; specifically, it is similar to the scheme when the insulating layer 12 is only provided on the surface of the positive electrode current collector 11 on the side close to the pole ear portion 40, and will not be described in detail here.

[0039] At this time, since an insulating layer 13 is also provided on the surface of the positive electrode current collector 11 away from the electrode ear portion 40, the total width of the positive electrode active material layer 12 and the insulating layer 13 is greater than the width of the negative electrode active material layer 22. Therefore, when the battery is pressurized, the overhang area of the negative electrode sheet can be supported by the insulating layer, so that the edge area of the negative electrode active material layer and the isolation membrane can be further tightly bonded.

[0040] In some embodiments, the insulating layer includes an inorganic material. In the present application, the inorganic material can use conventional inorganic materials known in the art. In some embodiments, the inorganic material includes at least one of barium sulfate (BaSO4), calcium silicate (CaSiO3), aluminum oxide (Al2O3), boehmite, magnesium hydroxide, aluminum hydroxide, silicon dioxide, magnesium oxide, and calcium orthosilicate (CaSiO4). In some embodiments, based on the total weight of the insulating layer, the weight percentage of the inorganic material is 60% to 93%. In some embodiments, based on the total weight of the insulating layer, the weight percentage of the inorganic material is 80% to 93%.

[0041] In some embodiments, the insulating layer further comprises an adhesive. The adhesive comprises at least one of polyvinylidene fluoride, polyurethane, polyacrylate, styrene-butadiene rubber, polyetherimide, sodium carboxymethyl cellulose, or acrylate. In some embodiments, the weight percentage of the adhesive is 7% to 40% based on the total weight of the insulating layer.

[0042] In some embodiments, the insulation layer has an impedance of 1 kΩ or greater, which can prevent electron transfer between the burrs generated during die-cutting of the positive electrode current collector and the insulation layer, thereby isolating the burrs of the positive electrode current collector from the isolation film. The insulation layer impedance can be tested using an internal resistance meter: wipe the contact head of the internal resistance meter with alcohol dipped in dust-free paper; turn on the power of the test fixture and adjust the contact head pressure to 0.5 MPa; place the test electrode on the lower contact head, start the device, and allow the upper contact head to press down on the electrode for 3-5 seconds; record the electrode resistance value, which is the insulation layer impedance.

[0043] In some embodiments, as Figure 1(a) to Figure 5(c) As shown, the width A of the portion where the outer edge 13a of the insulating layer extends beyond the outer edge 22a of the negative electrode active material layer satisfies: A ≤ 3mm. If the width A of the portion where the outer edge of the insulating layer extends beyond the outer edge of the negative electrode active material layer is too large, the width of the separator needs to be increased accordingly, resulting in a loss in the energy density of the electrochemical device. Moreover, even if A is greater than 3mm, there is no further improvement in the lithium deposition at the edge of the negative electrode, or the effect of further improvement in the lithium deposition at the edge of the negative electrode is weak. In some embodiments, the width A of the portion where the outer edge 13a of the insulating layer extends beyond the outer edge 22a of the negative electrode active material layer satisfies: 1.5mm ≤ A ≤ 3mm.

[0044] In some embodiments, as Figure 1(a) to Figure 5(c) As shown, the width A' of the insulating layer 13 satisfies: 0.2mm≤A'≤10mm. In the present application, the width of the insulating layer refers to the width of the insulating layer on one side of the positive electrode active material layer, that is, the width of the outer edge of the insulating layer exceeding the outer edge of the positive electrode active material layer. If the width A' of the insulating layer is too large, the width of the separator needs to be increased accordingly, resulting in a loss of energy density of the electrochemical device, and even if A' is greater than 10mm, there is no further improvement effect on the lithium deposition at the edge of the negative electrode, or the effect of further improving the lithium deposition at the edge of the negative electrode is weak; if the width A' of the insulating layer is too small, it cannot effectively reduce the burrs and material dropouts caused by punching, affecting the improvement effect on safety performance. In some embodiments, the width A' of the insulating layer 13 satisfies: 1mm≤A'≤5mm. In some embodiments, the width A' of the insulating layer 13 satisfies: 3mm≤A'≤5mm.

[0045] In the embodiment of the present application, the total width of the positive active material layer 12 and the insulating layer 13 is no greater than the width of the separator 30 to reduce the impact on the battery width and avoid loss of energy density of the electrochemical device.

[0046] The thickness of the insulating layer affects its support effect on the edge area of the negative electrode active material layer. In some embodiments, the thickness of the insulating layer T i The thickness T of the positive electrode active material layer p Satisfy: 0μm≤T p –T i ≤10μm. If the thickness of the insulating layer is too small relative to the thickness of the positive electrode active material layer, the supporting effect of the insulating layer on the edge area of the negative electrode active material layer will be weakened, affecting the improvement effect of lithium deposition at the edge of the negative electrode; if the thickness of the insulating layer is greater than the thickness of the positive electrode active material layer, it will be difficult to achieve the predetermined compaction density during cold pressing, thereby affecting the energy density of the electrochemical device. In some embodiments, the thickness of the insulating layer T i The thickness T of the positive electrode active material layer p Satisfy: 0μm≤T p –T i ≤2μm.

[0047] In some embodiments, the thickness of the insulating layer T i Satisfy: 10μm≤T i ≤T p .

[0048] It should be noted that the thickness of the insulating layer in this application is T i Refers to the thickness of the insulating layer provided on one side of the positive electrode current collector, and the thickness of the positive electrode active material layer T p It refers to the thickness of the positive electrode active material layer provided on one side of the positive electrode current collector.

[0049] In some embodiments, the negative electrode current collector is a metal, such as but not limited to copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0050] The negative electrode active material layer includes a negative electrode active material. The negative electrode active material can be selected from various materials that can be used as electrochemical devices and can be used to embed and de-embed active ions or materials that can be doped and de-doped with active ions. In some embodiments, the negative electrode active material includes at least one of a carbon material, a metal alloy, a lithium-containing oxide, and a silicon-containing material. The preparation method of the negative electrode can adopt a preparation method of a negative electrode that can be used in an electrochemical device. In some embodiments, in the preparation of the negative electrode slurry, a solvent is usually added, and the negative electrode active material is added with a negative electrode binder and, as needed, a conductive material and a thickener, and then dissolved or dispersed in the solvent to form a negative electrode slurry. The solvent is evaporated and removed during the drying process. The solvent is a solvent that can be used as a negative electrode active material layer, and the solvent is, for example, but not limited to, water. The thickener is a thickener that can be used as a thickener for the negative electrode active material layer, and the thickener is, for example, but not limited to, sodium carboxymethyl cellulose (abbreviated as CMC). The present application has no particular restrictions on the mixing ratio of the negative electrode active material, negative electrode binder, and thickener in the negative electrode active material layer, and their mixing ratio can be controlled according to the desired electrochemical device performance.

[0051] In some embodiments, the positive electrode current collector is a metal, such as but not limited to copper foil or aluminum foil.

[0052] The positive electrode active material layer includes a positive electrode active material. The positive electrode active material can be selected from various materials that can be used as positive electrode active materials of electrochemical devices and can reversibly embed and de-embed active ions. In some embodiments, the positive electrode active material includes LiCoO2, LiNiO2, LiMn2O4, LiCo 1-y M y O2、LiNi 1-y M y O2、LiMn 2-y M y O4、LiNi x Co y Mn z M 1-x-y-zAt least one of O2, wherein M is selected from one or more of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, and 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1. The preparation method of the positive electrode can adopt a preparation method of a positive electrode that can be used for an electrochemical device. In some embodiments, in the preparation of the positive electrode slurry, a solvent is usually added, and the positive electrode active material is added with a binder and, as needed, a conductive agent and a thickener are added, and then dissolved or dispersed in the solvent to form a positive electrode slurry. The solvent is evaporated and removed during the drying process. The solvent is a solvent that can be used as a positive electrode active material layer, such as, but not limited to, N-methylpyrrolidone (NMP). The binder is a binder that can be used as a positive electrode active material layer, such as, but not limited to, polyvinylidene fluoride (PVDF). The conductive agent is a conductive agent that can be used as a positive electrode active material layer, such as, but not limited to, Super P. The present application has no particular limitation on the mixing ratio of the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent in the positive electrode active material, and the mixing ratio can be controlled according to the desired performance of the electrochemical device.

[0053] The separator is a separator that can be used in electrochemical devices in the art. The present application has no particular restrictions on the material and shape of the separator.

[0054] The electrochemical device also includes an electrolyte. The electrolyte is any electrolyte known in the art that can be used in electrochemical devices. In some embodiments, the electrolyte includes an organic solvent, an electrolyte salt, and an additive. In some embodiments, the electrolyte salt is selected from a lithium salt. In some embodiments, the lithium salt is selected from LiPF6.

[0055] In some embodiments, the electrochemical device further comprises an outer packaging case, which is any outer packaging case that can be used for electrochemical devices in the art and is stable to the electrolyte used, such as, but not limited to, a metal outer packaging case.

[0056] In some embodiments, the tab portion includes multiple positive and negative tabs. Multiple tabs can increase the electron path during charging and discharging of the electrochemical device, reducing polarization and heat release in the battery cell. In some embodiments, the number of positive and negative tabs is equal to the number of battery cell layers, or the number of positive and negative tabs is half the number of battery cell layers. The positive and negative tabs overlap after the battery cell is wound and are each welded to the nickel-aluminum metal sheet.

[0057] (Electronic Devices)

[0058] The electronic device of the present application is any electronic device, such as but not limited to a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor. It should be noted that the electrochemical device of the present application is applicable to energy storage power stations, marine vehicles, and air vehicles in addition to the electronic devices listed above. Air vehicles include both air vehicles within the atmosphere and air vehicles outside the atmosphere.

[0059] In some embodiments, the electronic device comprises the electrochemical device described above.

[0060] The present application is further described below with reference to the examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. In the following specific examples of the present application, only examples in which the battery is a lithium-ion battery are shown, but the present application is not limited thereto. In the following examples and comparative examples, the reagents, materials, and instruments used, unless otherwise specified, can be commercially purchased or synthesized.

[0061] Example 1

[0062] Step S1: The positive electrode active material lithium cobalt oxide, the conductive agent Super P, and the binder PVDF are fully stirred and mixed in an appropriate amount of NMP at a weight ratio of 98:1:1 to obtain a uniformly mixed positive electrode slurry; the inorganic material BaSO4 and the binder PVDF are fully stirred and mixed in an appropriate amount of NMP at a weight ratio of 93:7 to obtain a uniformly mixed insulating slurry;

[0063] Step S2: The prepared positive electrode slurry is simultaneously coated on one side of the positive electrode current collector aluminum foil by an extrusion coater, with a coating thickness of 30 μm. The insulating slurry is coated on the side of the positive electrode slurry near the electrode ear along the edge of the positive electrode slurry, with a coating width of 3.5 mm and a coating thickness of 30 μm. After drying, the other side of the positive electrode current collector aluminum foil is coated in the same manner, dried, and cold pressed to obtain a positive electrode sheet.

[0064] Step S3: The negative electrode active material graphite, the binder styrene-butadiene rubber, and the thickener lithium carboxymethyl cellulose are thoroughly stirred and mixed in an appropriate amount of deionized water at a weight ratio of 97.5:1.3:1.2 to form a uniform negative electrode slurry. The negative electrode slurry is applied to one side of the negative electrode current collector copper foil using an extrusion coater. After drying, the negative electrode current collector copper foil is coated in the same manner on the other side. The negative electrode sheet is dried and cold pressed to obtain a negative electrode sheet.

[0065] Step S4: Using a PE porous polymer film as a separator, the separator is placed between the negative electrode sheet and the positive electrode sheet, with the positive electrode active material layer and the negative electrode active material layer facing each other through the separator, with the outer edge of the negative electrode active material layer extending beyond the outer edge of the positive electrode active material layer by 2 mm, and the outer edge of the insulating layer extending beyond the outer edge of the negative electrode active material layer by 1.5 mm;

[0066] In step S5, the stacked separator, negative electrode sheet and positive electrode sheet are wound to form an electrode assembly, which is then packaged, injected with electrolyte and allowed to stand to obtain an electrode assembly that is fully soaked, and then subjected to formation and capacity steps to obtain a lithium-ion battery.

[0067] Example 2-21

[0068] The preparation method is the same as that of Example 1, except that the parameters of the insulating layer, the positive electrode active material layer, and the negative electrode active material layer are adjusted in Example 2-21.

[0069] Example 22

[0070] The preparation method is the same as that of Example 1, except that in Example 22, the insulating slurry is coated on both sides of the positive electrode slurry along the edge of the positive electrode slurry (the side close to the pole ear and the side away from the pole ear), and the coating width of the insulating slurry on each side is 8 mm; at the same time, Example 22 also adjusts the parameters of other insulating layers, positive electrode active material layers, and negative electrode active material layers.

[0071] Example 23

[0072] The preparation method is the same as that of Example 22, except that the parameters of the insulating layer, the positive electrode active material layer, and the negative electrode active material layer are adjusted in Example 23.

[0073] Example 24

[0074] The preparation method is the same as that of Example 5, except that the parameters of the insulating layer, the positive electrode active material layer, and the negative electrode active material layer are adjusted in Example 24.

[0075] Comparative Example 1-2

[0076] The preparation method is the same as that of Example 1, except that the parameters of the insulating layer, the positive electrode active material layer, and the negative electrode active material layer are adjusted in Comparative Example 1-2. In Comparative Example 1-2, the outer edge of the negative electrode active material layer is further outward than the outer edge of the insulating layer.

[0077] The parameters of Examples 1-24 and Comparative Examples 1-2 are shown in Table 1.

[0078] Performance test of lithium-ion batteries:

[0079] Hotbox test:

[0080] 1) At 20±5℃, discharge the battery at 0.5C to 3.0V and leave it for 5 minutes;

[0081] 2) 0.5C charge to 4.45V, constant voltage charge to 0.05C (4.45V system);

[0082] 3) Stand at 20±5℃ for 60 min;

[0083] 4) Raise the temperature at a rate of 5°C / min±2°C / min to 130°C±2°C and maintain for 60 minutes;

[0084] 5) After the test is completed, check the appearance of the battery cell. If the battery is on fire, the test fails.

[0085] 25℃3C lithium deposition test:

[0086] The test was carried out at 25°C

[0087] 1) Leave the battery for 30 minutes;

[0088] 2) 0.5C charging to 4.45V, constant voltage charging to 0.05C;

[0089] 3) Leave it for 5 minutes;

[0090] 4) 0.5C discharge to 3V;

[0091] 5) Leave for 60 minutes;

[0092] 6) 3C charge to 4.45V, constant voltage charge to 0.05C;

[0093] 7) Leave it for 5 minutes;

[0094] 8) 1C discharge to 3V;

[0095] 9) Leave it for 5 minutes;

[0096] 10) Repeat steps 6 to 9 10 times;

[0097] 11) Leave for 120 minutes;

[0098] 12) 3C charge to 4.45V, constant voltage charge to 0.05C;

[0099] 13) Leave the battery for 5 minutes; observe the lithium deposition status of the lithium-ion battery and classify it according to the following standards:

[0100] After disassembling the lithium-ion battery, the negative electrode sheet is obtained. The golden yellow area is the normal area, and the white area is the lithium deposition area. After taking pictures with a high-magnification (20 times or more) microscope, the different areas are analyzed. If the proportion n of the white area in the total area satisfies 0<n<1%, it is recorded as "no lithium deposition"; if the proportion n of the white area in the total area satisfies 1%<n<10%, it is recorded as "mild lithium deposition"; if the proportion n of the white area in the total area satisfies 10%<n<100%, it is recorded as "severe lithium deposition".

[0101]

[0102] From the data analysis of Table 1, it can be obtained that when the outer edge of the negative electrode active material layer is further outward than the outer edge of the positive electrode active material layer in the facing position, an insulating layer is provided on the side of the positive electrode current collector close to the pole ear portion, and the inner edge of the insulating layer is in contact with or partially overlapped with the outer edge of the positive electrode active material layer, so that the outer edge of the insulating layer is flush with the outer edge of the negative electrode active material layer or is further outward than the outer edge of the negative electrode active material layer. At this time, the negative electrode lithium plating condition of the lithium ion battery can be improved and the pass rate of the thermal failure test can be improved. In Comparative Examples 1 and 2, although an insulating layer is provided on the side of the positive electrode current collector close to the pole ear portion, after the battery cell is made, the outer edge of the negative electrode active material layer is further outward than the outer edge of the insulating layer. Therefore, the insulating layer cannot provide support for the edge area of the negative electrode active material layer, and negative electrode lithium plating is prone to occur and the pass rate of the thermal failure test is low.

[0103] The thickness of the insulating layer affects the improvement effect of negative electrode lithium deposition and the pass rate of the lithium ion battery thermal failure test. From the data of Examples 8 to 12, it can be seen that if the thickness of the insulating layer is too small, the improvement effect of negative electrode lithium deposition and the pass rate of the lithium ion battery thermal failure test will be poor.

[0104] The composition and impedance of the insulating layer affect the improvement in the pass rate of the lithium-ion battery thermal failure test. The data from Examples 9, 14, and 21 indicate that if the inorganic material mass fraction of the insulating layer is too small, the insulating layer impedance is low, and the improvement in the pass rate of the lithium-ion battery thermal failure test is poor.

[0105] The above detailed description describes multiple exemplary embodiments, but this document is not intended to be limited to the explicitly disclosed combinations. Therefore, unless otherwise stated, the various features disclosed herein can be combined to form multiple additional combinations that are not shown for the sake of simplicity.

Claims

1. An electrochemical device comprising: A negative electrode comprising a negative electrode current collector, wherein a negative electrode active material layer is provided on at least one surface of the negative electrode current collector; A positive electrode comprising a positive electrode current collector, wherein a positive electrode active material layer is provided on at least one surface of the positive electrode current collector, and an insulating layer is provided on a surface of the positive electrode current collector on a side close to a tab portion, wherein the tab portion is formed by cutting out a hollow foil area at an edge of the positive electrode current collector, and the tab portion protrudes from the positive electrode current collector; a separator disposed between the negative electrode and the positive electrode, wherein the positive electrode active material layer and the negative electrode active material layer face each other via the separator; in, The outer edge of the negative electrode active material layer is located further outward than the outer edge of the positive electrode active material layer at the facing position; The inner edge of the insulating layer is in contact with or partially overlaps with the outer edge of the positive electrode active material layer, and the outer edge of the insulating layer is flush with or further outward than the outer edge of the negative electrode active material layer. i The thickness T of the positive electrode active material layer p Satisfy: 0μm≤T p –T i ≤10μm.

2. The electrochemical device according to claim 1, wherein The insulating layer is provided on a surface of the positive electrode current collector at a side away from the electrode ear portion.

3. The electrochemical device according to claim 1 or 2, wherein The width A of the portion where the outer edge of the insulating layer exceeds the outer edge of the negative electrode active material layer satisfies: A≤3 mm.

4. The electrochemical device according to claim 1 or 2, wherein The width A' of the insulating layer satisfies: 0.2 mm ≤ A' ≤ 10 mm.

5. The electrochemical device according to claim 1 or 2, wherein The width B of the portion where the outer edge of the negative electrode active material layer exceeds the outer edge of the positive electrode active material layer satisfies the following: 0.2 mm ≤ B ≤ 5 mm.

6. The electrochemical device according to claim 1 or 2, wherein: The thickness T of the insulating layer i The thickness T of the positive electrode active material layer p Satisfy: 0μm≤T p –T i ≤2μm.

7. The electrochemical device according to claim 1 or 2, wherein: The thickness T of the insulating layer i Satisfy: 10μm≤T i ≤T p .

8. The electrochemical device according to claim 1 or 2, wherein the insulating layer comprises an inorganic material and a binder, The inorganic material includes at least one of barium sulfate, calcium silicate, aluminum oxide, boehmite, magnesium hydroxide, aluminum hydroxide, silicon dioxide, magnesium oxide, and calcium orthosilicate, and the adhesive includes at least one of polyvinylidene fluoride, polyurethane, polyacrylate, styrene-butadiene rubber, polyetherimide, sodium carboxymethyl cellulose, or acrylate.

9. The electrochemical device according to claim 8, wherein Based on the total weight of the insulating layer, the weight percentage of the inorganic material is 60% to 93%, and the weight percentage of the adhesive is 7% to 40%.

10. The electrochemical device according to claim 1 or 2, wherein The impedance of the insulating layer is greater than or equal to 1 KΩ.

11. An electronic device comprising the electrochemical device according to any one of claims 1 to 10.

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